<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>table方式</title>
  <style>
    .outer {
      display: table;
    }

    .inner {
      width: 300px;
      height: 300px;
      background: lightgreen;
    }
    .mid {
      display: table-cell;
      width: 100%;
      background-color: lightyellow;
    }
  </style>
</head>
<body>
  <div class="outer">
    <div class="inner left">left</div>
    <div class="inner mid">mid</div>
    <div class="inner right">right</div>
  </div>
</body>
</html>